/*
 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 *
 *
 */

package javax.script;

import java.io.Reader;
import java.util.Map;
import java.util.Iterator;

/**
 * Provides a standard implementation for several of the variants of the <code>eval</code>
 * method.
 * <br><br>
 * <code><b>eval(Reader)</b></code><p><code><b>eval(String)</b></code><p>
 * <code><b>eval(String, Bindings)</b></code><p><code><b>eval(Reader, Bindings)</b></code>
 * <br><br> are implemented using the abstract methods
 * <br><br>
 * <code><b>eval(Reader,ScriptContext)</b></code> or
 * <code><b>eval(String, ScriptContext)</b></code>
 * <br><br>
 * with a <code>SimpleScriptContext</code>.
 * <br><br>
 * A <code>SimpleScriptContext</code> is used as the default <code>ScriptContext</code>
 * of the <code>AbstractScriptEngine</code>..
 *
 * @author Mike Grogan
 * @since 1.6
 */
public abstract class AbstractScriptEngine implements ScriptEngine {

  /**
   * The default <code>ScriptContext</code> of this <code>AbstractScriptEngine</code>.
   */

  protected ScriptContext context;

  /**
   * Creates a new instance of AbstractScriptEngine using a <code>SimpleScriptContext</code>
   * as its default <code>ScriptContext</code>.
   */
  public AbstractScriptEngine() {

    context = new SimpleScriptContext();

  }

  /**
   * Creates a new instance using the specified <code>Bindings</code> as the
   * <code>ENGINE_SCOPE</code> <code>Bindings</code> in the protected <code>context</code> field.
   *
   * @param n The specified <code>Bindings</code>.
   * @throws NullPointerException if n is null.
   */
  public AbstractScriptEngine(Bindings n) {

    this();
    if (n == null) {
      throw new NullPointerException("n is null");
    }
    context.setBindings(n, ScriptContext.ENGINE_SCOPE);
  }

  /**
   * Sets the value of the protected <code>context</code> field to the specified
   * <code>ScriptContext</code>.
   *
   * @param ctxt The specified <code>ScriptContext</code>.
   * @throws NullPointerException if ctxt is null.
   */
  public void setContext(ScriptContext ctxt) {
    if (ctxt == null) {
      throw new NullPointerException("null context");
    }
    context = ctxt;
  }

  /**
   * Returns the value of the protected <code>context</code> field.
   *
   * @return The value of the protected <code>context</code> field.
   */
  public ScriptContext getContext() {
    return context;
  }

  /**
   * Returns the <code>Bindings</code> with the specified scope value in
   * the protected <code>context</code> field.
   *
   * @param scope The specified scope
   * @return The corresponding <code>Bindings</code>.
   * @throws IllegalArgumentException if the value of scope is invalid for the type the protected
   * <code>context</code> field.
   */
  public Bindings getBindings(int scope) {

    if (scope == ScriptContext.GLOBAL_SCOPE) {
      return context.getBindings(ScriptContext.GLOBAL_SCOPE);
    } else if (scope == ScriptContext.ENGINE_SCOPE) {
      return context.getBindings(ScriptContext.ENGINE_SCOPE);
    } else {
      throw new IllegalArgumentException("Invalid scope value.");
    }
  }

  /**
   * Sets the <code>Bindings</code> with the corresponding scope value in the
   * <code>context</code> field.
   *
   * @param bindings The specified <code>Bindings</code>.
   * @param scope The specified scope.
   * @throws IllegalArgumentException if the value of scope is invalid for the type the
   * <code>context</code> field.
   * @throws NullPointerException if the bindings is null and the scope is
   * <code>ScriptContext.ENGINE_SCOPE</code>
   */
  public void setBindings(Bindings bindings, int scope) {

    if (scope == ScriptContext.GLOBAL_SCOPE) {
      context.setBindings(bindings, ScriptContext.GLOBAL_SCOPE);
      ;
    } else if (scope == ScriptContext.ENGINE_SCOPE) {
      context.setBindings(bindings, ScriptContext.ENGINE_SCOPE);
      ;
    } else {
      throw new IllegalArgumentException("Invalid scope value.");
    }
  }

  /**
   * Sets the specified value with the specified key in the <code>ENGINE_SCOPE</code>
   * <code>Bindings</code> of the protected <code>context</code> field.
   *
   * @param key The specified key.
   * @param value The specified value.
   * @throws NullPointerException if key is null.
   * @throws IllegalArgumentException if key is empty.
   */
  public void put(String key, Object value) {

    Bindings nn = getBindings(ScriptContext.ENGINE_SCOPE);
    if (nn != null) {
      nn.put(key, value);
    }

  }

  /**
   * Gets the value for the specified key in the <code>ENGINE_SCOPE</code> of the
   * protected <code>context</code> field.
   *
   * @return The value for the specified key.
   * @throws NullPointerException if key is null.
   * @throws IllegalArgumentException if key is empty.
   */
  public Object get(String key) {

    Bindings nn = getBindings(ScriptContext.ENGINE_SCOPE);
    if (nn != null) {
      return nn.get(key);
    }

    return null;
  }


  /**
   * <code>eval(Reader, Bindings)</code> calls the abstract
   * <code>eval(Reader, ScriptContext)</code> method, passing it a <code>ScriptContext</code>
   * whose Reader, Writers and Bindings for scopes other that <code>ENGINE_SCOPE</code>
   * are identical to those members of the protected <code>context</code> field.  The specified
   * <code>Bindings</code> is used instead of the <code>ENGINE_SCOPE</code>
   *
   * <code>Bindings</code> of the <code>context</code> field.
   *
   * @param reader A <code>Reader</code> containing the source of the script.
   * @param bindings A <code>Bindings</code> to use for the <code>ENGINE_SCOPE</code> while the
   * script executes.
   * @return The return value from <code>eval(Reader, ScriptContext)</code>
   * @throws ScriptException if an error occurs in script.
   * @throws NullPointerException if any of the parameters is null.
   */
  public Object eval(Reader reader, Bindings bindings) throws ScriptException {

    ScriptContext ctxt = getScriptContext(bindings);

    return eval(reader, ctxt);
  }


  /**
   * Same as <code>eval(Reader, Bindings)</code> except that the abstract
   * <code>eval(String, ScriptContext)</code> is used.
   *
   * @param script A <code>String</code> containing the source of the script.
   * @param bindings A <code>Bindings</code> to use as the <code>ENGINE_SCOPE</code> while the
   * script executes.
   * @return The return value from <code>eval(String, ScriptContext)</code>
   * @throws ScriptException if an error occurs in script.
   * @throws NullPointerException if any of the parameters is null.
   */
  public Object eval(String script, Bindings bindings) throws ScriptException {

    ScriptContext ctxt = getScriptContext(bindings);

    return eval(script, ctxt);
  }

  /**
   * <code>eval(Reader)</code> calls the abstract
   * <code>eval(Reader, ScriptContext)</code> passing the value of the <code>context</code>
   * field.
   *
   * @param reader A <code>Reader</code> containing the source of the script.
   * @return The return value from <code>eval(Reader, ScriptContext)</code>
   * @throws ScriptException if an error occurs in script.
   * @throws NullPointerException if any of the parameters is null.
   */
  public Object eval(Reader reader) throws ScriptException {

    return eval(reader, context);
  }

  /**
   * Same as <code>eval(Reader)</code> except that the abstract
   * <code>eval(String, ScriptContext)</code> is used.
   *
   * @param script A <code>String</code> containing the source of the script.
   * @return The return value from <code>eval(String, ScriptContext)</code>
   * @throws ScriptException if an error occurs in script.
   * @throws NullPointerException if any of the parameters is null.
   */
  public Object eval(String script) throws ScriptException {

    return eval(script, context);
  }

  /**
   * Returns a <code>SimpleScriptContext</code>.  The <code>SimpleScriptContext</code>:
   * <br><br>
   * <ul>
   * <li>Uses the specified <code>Bindings</code> for its <code>ENGINE_SCOPE</code>
   * </li>
   * <li>Uses the <code>Bindings</code> returned by the abstract <code>getGlobalScope</code>
   * method as its <code>GLOBAL_SCOPE</code>
   * </li>
   * <li>Uses the Reader and Writer in the default <code>ScriptContext</code> of this
   * <code>ScriptEngine</code>
   * </li>
   * </ul>
   * <br><br>
   * A <code>SimpleScriptContext</code> returned by this method is used to implement eval methods
   * using the abstract <code>eval(Reader,Bindings)</code> and <code>eval(String,Bindings)</code>
   * versions.
   *
   * @param nn Bindings to use for the <code>ENGINE_SCOPE</code>
   * @return The <code>SimpleScriptContext</code>
   */
  protected ScriptContext getScriptContext(Bindings nn) {

    SimpleScriptContext ctxt = new SimpleScriptContext();
    Bindings gs = getBindings(ScriptContext.GLOBAL_SCOPE);

    if (gs != null) {
      ctxt.setBindings(gs, ScriptContext.GLOBAL_SCOPE);
    }

    if (nn != null) {
      ctxt.setBindings(nn,
          ScriptContext.ENGINE_SCOPE);
    } else {
      throw new NullPointerException("Engine scope Bindings may not be null.");
    }

    ctxt.setReader(context.getReader());
    ctxt.setWriter(context.getWriter());
    ctxt.setErrorWriter(context.getErrorWriter());

    return ctxt;

  }
}
